Plunger vs. Diaphragm Pump: How to Select the Best Pump
by Steve Babcock, VP of Engineering, on Aug 11, 2020
What’s the difference between plunger and diaphragm pumps, and how can you know which type of pump is best for your unique application?
Each serves a unique purpose and they’re typically not interchangeable. That’s especially true with plunger pumps and diaphragm pumps. First, we’ll give a brief explanation of how each pump works. Then, we’ll outline the pros and cons of each and how to know which one to choose for your application.
How do Plunger Pumps Work?
Plunger pumps — sometimes referred to as piston pumps — have a reciprocating plunger that moves back and forth, forcing liquids through a set of valves. Some simple examples in our everyday lives might include a bicycle pump, spray bottle, or squirt gun.
Commercially, plunger pumps are commonly used in cleaning, disinfection, pest control, agriculture, and other applications in their electrically powered equipment such as pressure washers, misters and sprayers.
How do Diaphragm Pumps Work?
There are similarities between plunger pumps and diaphragm pumps. Both are considered reciprocating pumps, however, the end of the plunger in a diaphragm pump is connected to a flexible diaphragm that flexes back and forth. The human heart, for example, is a type of naturally occurring diaphragm pump.
Commercially, however, they are commonly used for dispensing water and are best suited for lower PSI.
The Pros & Cons of Plunger Pumps vs. Diaphragm Pumps
Another notable difference between plunger and diaphragm pumps that must be considered is the power source. A diaphragm pump can be manufactured to accommodate a gas-powered engine or electric-powered motor. However, a gas-powered diaphragm pump is required to achieve the desired output and power needed for commercial use. Those using electric power are typically sold for residential use in small hand-held sprayers, RV sinks, and other low-impact use.
Piston or plunger pumps are also available as 12V battery-powered or gas powered units. Unlike diaphragm pumps, however, there are some manufacturers that engineer their electric battery-powered plunger pumps to perform as well or better than gas-powered diaphragm pumps in rugged, commercial applications. As such, for the purpose of this article, we’ll compare commercial electric plunger pumps vs. gas-powered diaphragm pumps.
Positive displacement pumps refers to their ability to capture and move fluid forward through the system. Plunger pumps have a stable flow by use of a pressure regulator. The liquids are dispensed through the plunger pump system at a steady, fixed flow rate due to rigid components, providing consistent, even coverage. Diaphragm pumps also require a pressure regulator but, because some of the components are flexible, the flow is also “flexible,” meaning they’re notorious for losing pressure and having inconsistent flow.
High Pressure Capabilities
Once again, the flexible components in a diaphragm pump can be its downfall, especially when it comes to applications requiring high PSI. The flexible diaphragm can rupture under high pressure whereas a plunger pump is engineered to withstand repeated high-pressure use. If you’re constantly replacing diaphragm pumps used in your high PSI applications, you may simply need to switch to a more durable plunger pump for an easy solution.
Equipment that uses 12V motors are much quieter than gas engines. If you’re in the pest control industry, for example, but your clients don’t want to call attention to the services you provide to their residences, a 12V pump system will quietly do the job.
Quiet operation also benefits lawn care professionals by increasing the hours of service available to them. In many areas, there are noise restrictions that limit the hours that gas engine diaphragm pumps can be operated. A 12V plunger pump system would not be controlled by this rule.
Unlike a typical centrifugal pump which requires priming to remove air from the pump chamber and avoid becoming inoperable, both the plunger pump and diaphragm pump will self prime. The step of priming a pump isn’t always straightforward, and inexperienced operators may encounter issues, losing precious time and raising labor costs.
Battery technology has advanced significantly in recent years. Today’s 12V plunger pump systems use batteries with extended run times that outlast the capacity of many gas-powered diaphragm pump engines. The operator doesn’t have to stop in the middle of a job to refuel or adjust the throttle, and safety is improved by not having to transport volatile substances. With a 12V system, operators can even ‘refill’ their batteries while driving between jobs.
The battery used in plunger pump systems is comparable to a marine battery and is about the same size. Therefore, the battery-powered unit is much more compact and maneuverable than a gas-powered diaphragm unit, making jobs less taxing on operators and improving safety. If you’re looking for a pump with a smaller footprint, the plunger pump wins out.
If you’re like many organizations that have green initiatives, battery-powered 12V equipment offers the benefits of ‘green’ technology. Concern over gas prices, oil dependency, and pollution will continue to rise, and the latest 12V plunger pump technology is an environmentally responsible power source. Users of 12V equipment may receive more business as a result of these trends in the market compared to diaphragm pumps.
The bottom line is that electric-powered plunger pumps may help your bottom line. Gas engines typically cost more than batteries, and you also need to purchase fuel on an ongoing basis which can experience price volatility over time. Marine-type batteries can be recharged again and again and are generally price-stable. Over time you’ll likely experience significant cost savings with a battery-powered plunger pump, not only from limiting fuel consumption but because of fewer breakdowns, downtime, and repairs.
And the Winner Is…
For commercial cleaning, disinfection, pest control, agriculture, lawn care, and other pump sprayers and misters, an electric-powered plunger pump is clearly the best option. There are several other types of pumps in the industry, too. Learn about seven of the most common types in our Pump Comparison Cheat Sheet below.